Copper-oxide rectifiers



Patented Sept. 26, 1

East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing.Application September 27, 1940,

Serial No. 358.609

4 Claims. (Cl. 175-366) My invention relates to contact r'ectiflers andin particular to the methods of making electrical contacts to theoperating surface-areas of such rectifiers.

One object of my invention is to provide a method for making electricalcontact to surfaces of contact rectifiers in-such a way that theelectrical resistance of the contact will not be altered substantiallyby exposure to moisture and humid atmospheres.

Another object of my invention is to provide an improved method formaking contact to the oxide surface of copper-oxide rectifiers.

Still another object of my invention is to provide an intermediate layerbetween the oxidized surface of a copper-oxide rectifier and a sprayedmetal terminal area adapted to conduct current satisfactorily to therectifier.

Other objects of my invention will becomeapparent upon reading thefollowing specification.

A well known form of electrical rectifier employs an oxidized disk ofmetallic copper-as is described in Grondahl'Patent 1,640,335, assignedto the Union Switch 8,: Signal Company, Swissvale, Pennsylvania. In suchrectifiers, it is necessary to provide some arrangement for conductingcurrent readily into the oxidized surface on the copper, such contactsbeing made in accordance with the description in the Grondahl patent bycoating the copper oxide surface with powdered graphite and pressing alead washer into firm contact thereon. In the process of factoryproduction of such rectifiers the graphite has been applied in the formof a preparation having the trade name Aquadag, manufactured by theAcheson Colloids Corporation, Port Huron, Michigan. While satisfactoryfor most purposes, it has been found that when rectiflers coated withAquadag have been employed in places where they were exposed to steam orother vapors, or.

even indamp and humid places such as garages stantially 5 to 15% ofgraphite in a solvent of a high flash point naptha or the like. Thepercentage constituency depends upon the type of use. For spraying, alarger amount of solvent is employed than for painting on as in the caseof Aquadag. For example, the graphite product described in Bartell2,176,879 assigned to Acheson Colloids Corporation, New York, N. Y.,made-up to contain from .7.5 to 10% of solids by weight may be, used {orcase Schoop-sprayed tin) will be-found in the- Aumann Patent 1,801,831.

An alternative method of applying the graphite is to employ a suspensionof colloidal graphite in carbon tetrachloride in place of the mixture ofgraphite with high flash point naptha already described. However, thecarbon tetrachloride suspension has proved less satisfactory formed bythe above described process with those in which Aquadag is used as thecoating agent have clearly shown a great superiority for the former.Thus after four days in a humid atmosphere, ten rectifier platesof-copper measuring 4 x 12" x .050" which employ the Aquadag treatmentshow an average increase of approximately in resistance in thehighlyconductive direction at 12% ampere load, while ten exactly similarplates in the making ofv which the-naptha solvent graphite was usedaveraged an increase of only about 1%'in the same period. Furthermore,the deviations in forward resistance from the average were far greateramong the rectifiers coated with Aquadag than;it was between therectiflers coated with the naptha suspension graphite; the range ofvariation among the Aquadag rectiflers at the end of the above-mentionedfour day tests was of the order of of the original resistance, while therange of resistance in. the-naptha solvent rectiflers was only about 14%of the initial resistance. The greater constancy, and greater uniformityof forward resistance resulting from the substitution of naptha solventgraphite coats for Aquadag coats is thus evident.

While I have described one embodiment oi my invention in accordance withthe patent stat- United States Patent 2 utes, its broad principles arecapable of other applications which will be self-evident to thoseskilled in the art. Broadly speaking, I believe my contribution to therectifier art here described to lie in the removal from the liquid inwhich colloidal graphite particles are suspended to form v a coatingmixture or hygroscopic and harmful chemical constituents. I also believeit to be evident to those skilled in the art that the method .which Ihave developed for forming protective comprises applying to the oxidizedsurface a coating of colloidal graphite suspended in high flash- 2. Themethod of producing an electrical contact surface for copper oxiderectifier-s which comprises applying to the oxidized surface a coatingof colloidal graphite suspended in high flashpoint naptha, freeing thecoating of the naptha,

and Schoop-spraying the outer surfac of the coating with tin.

3. The method of forming an electrical contact to a conductor body whichcomprises coating the body with colloidal graphite suspended in a highflashpoint naptha solvent and freeing the coating of the solvent, andcovering at least point naptha. freeing the coating 0! the naptha, 20

and covering the outer suri'ace oi the coating with a metal layer. 1

a portion or the coating with a layer of metal.

4. A rectifier comprising metallic copper having a portion oi" itssurface oxidized and coated with a layer of colloidal g aphite appliedwhile suspended in a high nashpoint naptha solvent, and covered with anouter layer or metal. 7

CARL C. HEIN.

